Conventionally, a level shifter always comprises a GGNMOS (gate-grounded NMOS)for ESD (Electrostatic discharge) protection. Specifically, the GGMOS has a parasitic BJT therein, such that the ESD current can be leaked to a ground via the parasitic BJT. However, the parasitic BJT does not work well if the GGNMOS is made by a 3D process such as a FinFET process.
Therefore, another solution is to provide a switch circuit (or named a tie-low circuit) coupled to a gate terminal of the GGNMOS. However, such structure has some defects. One of which is that the gate terminal of the GGNMOS may receive a floating voltage caused by other sources while the switch circuit is non-active. Such floating voltage may turn on the GGNMOS thus causes un-desired leakage currents.